Pipe or plumbing systems often include access openings or ports that allow the interior of the pipes of the pipe system to be inspected and/or cleaned. Access opening configurations for such pipe systems can vary in size and shape, although many configurations are standardized. In one common configuration, an access opening is provided at the end of a relatively short section (often referred to as a “clean-out”) of cylindrical pipe that extends away from the axis of the main pipe section. Clean-outs may extend from a main pipe section at any angle. Those that extend approximately 90 degrees from the main pipe section are commonly called “clean-out tees” (referring to the T-shape created by the intersecting pipe sections).
Many clean-outs have a standard configuration in which the inner surface of the end of the clean-out is threaded adjacent the access opening so as to receive a correspondingly threaded clean-out end cap or plug that closes off the access opening. This plug is intended to be removed and reinstalled as necessary for access to the interior of the pipe system. In many pipe systems, the constant removal and reinstallation of a clean-out plug damages portions of the threads of the corresponding clean-out. Such damage may include cross-threading, which is the result of the two mating threads attempting to engage each other when out of alignment. Cross-threading occurs when the external threads of the clean-out plug tend to cross over the crests of the internal threads of the clean-out. This can produce deformation of the clean-out threads, primarily at the leading and middle portions of the threaded area.
Thread damage is also a problem if the clean-out plug is not removed very often, and the clean-out plug and/or the clean-out becomes corroded or otherwise seized together. The removal process may then involve destructive removal steps, which may lead to significant damage to the internal threads of the clean-out. However damaged, it may be difficult or impossible to reinstall a conventional clean-out plug to appropriately close off the pipe system.
In the past, various types of replacement clean-out plugs have been proposed for use with pipe system clean-outs. For example, U.S. Pat. No. 5,035,266 (“the '266 patent”) describes a replacement mechanical plug device for sealing pipe system access openings having threaded inner surfaces. The plug device described by the '266 patent includes a radially expandable O-ring structure that has an outer circumference configured to seal a pipe system clean-out. However, this device suffers from several shortcomings. Most notably, the O-ring structure described by the '266 patent includes an external surface configured, when expanded, to mate within the threaded portion of the clean-out. As noted above, the threaded portion of the clean-out is often damaged by removal and reinstallation of the original clean-out plug. As a result, the replacement mechanical plug described by the '266 patent will not provide optimal sealing of a threaded clean-out where the treads have been damaged, such as by cross-threading. Additionally, the O-ring structure of the '266 patent is not attached to the plug device, and after extended usage the expanded O-ring structure tends to adhere to the interior of the clean-out such that when the clean-out plug is removed, the plug pulls through the O-ring and the O-ring remains attached to the inside of the clean-out.
There is a need, therefore, for an improved clean-out plug that is configured to seal the access opening of a threaded pipe system clean-out. The clean-out plug should be configured to seal the access opening despite damage to the clean-out threads. The clean-out plug should also provide improved sealing around the internal periphery of the clean-out, and should be capable of being removed without damaging the plug.